The present invention relates to shaft seals for pintle-type valves; more particularly to seals for solenoid-actuated pintle valves for metering the flow of gases; and most particularly to a gas leakage containment system including an elastomeric boot or folded diaphragm for containing gases leaked from a pintle shaft bore in the valve body, thereby preventing undesirable entry of such gases into the actuator or the atmosphere.
It is well known to use pintle-type valves to meteringly control the flow of gases from one distributor into another. For example, in the automotive art a variable-flow control valve connecting the exhaust manifold with the intake manifold of an internal combustion engine is used to permit selective recirculation of a portion of an engine""s exhaust gas into the fuel intake stream. Such recirculation is beneficial for reducing the burn temperature of the fuel mix in the engine to reduce formation of nitrogen and sulfur oxides which are significant components of smog. Such a valve is known in the art as an exhaust gas recirculation (EGR) valve. In fuel cells, a three-way pintle-type valve may be used to regulate the flow of reformate to either a waste burner or the reaction chamber.
Typically, a pintle-type gas metering valve has a valve body enclosing a chamber. In an EGR valve, this chamber is disposed between a first port in the exhaust manifold and a second port in the intake manifold; a valve seat dividing the chamber between the two ports; a pintle shaft having a valve head fitted to the valve seat and extending from the valve head through a bearing mounted in a third port in a sidewall of the valve body; a spring-retained bearing splash shield; and a solenoid actuator mounted on the exterior of the valve body and having an armature into which the outer end of the valve pintle extends. Typically, a space between the valve body and the valve actuator containing the splash shield is exposed to atmospheric conditions.
The exhaust gas managed by an EGR valve is moisture-laden, corrosive, and dirty. If this gas is allowed to enter the valve actuator, for example, by leaking along the pintle shaft, then internal corrosion, malfunction, and ultimate failure of the actuator can result. Such failure can lead to emission non-compliance and can incur significant cost to a vehicle manufacturer if a recall is required.
The gas managed by a fuel cell valve typically is hydrogen, which is very difficult to seal against because of its molecular size and which can be violently explosive in. combination with oxygen. Thus, shaft leakage to the atmosphere is highly undesirable.
In pintle-type gate valves, the shafts may be sealed via well-known packing glands, through which the pintle motion is substantially rotary. Such glands are not practical in metering valves actuated by low-force solenoids in which the pintle motion is entirely axial because adequate packing would create unacceptably large frictional forces on the pintle, requiring very large and expensive actuators.
In many prior art solenoid-actuated gas control valves in use today, a compromise has been reached wherein leak rates of  less than 0.2 grams/second are accepted, to minimize shaft frictional loading and allow low hysteresis actuation of the valve. However, ever more stringent emission regulations and the advent of fuel cells in the automotive industry make this compromise no longer acceptable. This has increased the industry need for a time-proven, cost-effective actuator and valve which can overcome the historically impossible obstacle of attaining zero leakage from the shaft.
What is needed is a gas leakage containment system disposed between a pintle-type valve and its actuator which prevents gas and/or moisture from intruding into the actuator and/or escaping to the atmosphere, without impairing efficiency, size, and performance of the valve and actuator. Preferably, such a containment system is simple and inexpensive to fabricate and install.
The present invention is directed to a shaft leakage containment system comprising a novel shaft seal for installation on an interrupted pintle shaft in a pintle-type valve, such as an exhaust gas recirculation valve for an internal. combustion engine or a diverter valve for a fuel cell, for preventing leakage of gas and/or moisture along the pintle shaft into the actuator and/or the atmosphere. The system comprises two elements: a positive vapor block in the form of a sealed, impermeable, elastomeric boot or folded diaphragm disposed across the pintle shaft interruption, and means for sealingly securing the boot or diaphragm to the valve body and to the interrupted pintle shaft.